High aspect ratio materials such as fibers, rods, filaments, etc. are often coated with a polymeric material for protective or other purposes. For instance, optical fibers as are used to transmit light in various applications, including communications, typically are coated with one or more polymeric layers that are designed to protect the optical fibers from moisture and abrasion, to reduce microbending losses, to allow easier handling of the fiber and to simplify identification of the individual fibers in a bundle (e.g. coloring.)
In a typical method for coating an optical fiber, a liquid photocurable polymeric material is first applied to the surface of the fiber. This coating is then cured, for instance by irradiating the fiber with radiant energy, e.g., ultraviolet energy.
A variety of devices have been designed for irradiative curing of such coatings. For instance, U.S. Pat. No. 4,710,638 to Wood describes an apparatus for treating polymeric coatings with radiant energy. The apparatus includes first and second reflectors that together form a single ellipse, a light source positioned at one focus of the ellipse formed by the two reflectors and an auxiliary reflector near the second focus of the ellipse. A polymer-coated fiber can be positioned at the second focus and radiant energy from the light source can cure the polymer. U.S. Pat. Nos. 6,419,749 and 6,511,715, both to Rhoades describe a similar device that includes two reflectors that together form a single ellipse and a light source positioned at one focus of the ellipse. The devices of Rhoades also include first and second concentric tubes. Ultraviolet light from the light source passes through the first tube to cure the coating on a filament passing therethrough, and the second concentric tube reflects infrared light and passes ultraviolet light to prevent burning and destroying the coating on the filament as it passes through the first tube. U.S. Pat. No. 6,626,561 to Carter, et al. describes another similar device, with the inclusion of end reflectors on the first reflector that can have mounts for the lamp bulb.
All such previously known optical systems include the basic design as illustrated in FIG. 1 and FIG. 2 that includes two elliptical-shaped reflectors 1, 25, which are positioned such that the cross section of the primary and secondary reflectors form a single ellipse. As the primary 1 and secondary 25 reflectors form a single ellipse, the near focal point 2 of the primary reflector 1 is coincident with the far focal point 2 of the secondary reflector 25. Likewise, the far focal point 4 of the primary reflector 1 is coincident with the near focal point 4 of the secondary reflector 25. The primary and secondary reflectors share the same major axis. A light source 10 is suspended in the elliptical space, at or near the near focal point 2 on the major axis that is closest to the primary reflector 1. The material to be exposed to the radiant energy, such as an optical fiber, is located in the elliptical space substantially coincident with the focal point 4 that is farthest from the primary reflector 1, for instance within a quartz tube 7.
While such devices describe various improvements in the art, problems still exist with such devices. For instance, as manufacturing production rates are limited by the efficiency of the radiant energy transfer to the material to be cured or exposed, the manufacturer must add additional radiant exposure units to improve production rates, which increases capital costs, operating costs, and maintenance costs. Attempts have been made to improve the efficiency of the coating and curing process by techniques such as addition of the additional reflectors to the system as described by Woods and Carter, et al., by modifying the polymeric composition and/or the coating method, and by selecting optimal wavelengths of the curing radiation.
Room for further improvement in the art exists. For instance, what are needed in the art are devices that provide more efficient use of the radiant energy that cures the polymer.